From affbe30b4188ab11417d156fe2d430f9c1a426b0 Mon Sep 17 00:00:00 2001
From: andri lim <jangko128@gmail.com>
Date: Wed, 9 Oct 2019 08:51:53 +0700
Subject: [PATCH] implement compile time helpers

---
 stint/io.nim                          |  8 +++-----
 stint/private/compiletime_helpers.nim |  9 +++++++++
 stint/private/endians2_priv.nim       | 15 +++++----------
 3 files changed, 17 insertions(+), 15 deletions(-)
 create mode 100644 stint/private/compiletime_helpers.nim

diff --git a/stint/io.nim b/stint/io.nim
index 35aa61d..854bc8a 100644
--- a/stint/io.nim
+++ b/stint/io.nim
@@ -10,7 +10,7 @@
 import
   ./private/datatypes,
   ./private/int_negabs,
-  ./private/[int_bitwise_ops, uint_bitwise_ops],
+  ./private/compiletime_helpers,
   ./intops,
   typetraits, algorithm
 
@@ -285,13 +285,11 @@ proc dumpHex*(x: Stint or StUint, order: static[Endianness] = bigEndian): string
   result = newString(2*size)
 
   when nimvm:
-    type DT = type x.data.leastSignificantWord
     for i in 0 ..< size:
       when order == system.cpuEndian:
-        let pos = (i * 8)
+        let byte = x.data.getByte(i)
       else:
-        let pos = ((size - (i + 1)) * 8)
-      let byte = (x.data shr pos).leastSignificantWord and 0xFF.DT
+        let byte = x.data.getByte(size - 1 - i)
       result[2*i] = hexChars[int byte shr 4 and 0xF]
       result[2*i+1] = hexChars[int byte and 0xF]
   else:
diff --git a/stint/private/compiletime_helpers.nim b/stint/private/compiletime_helpers.nim
new file mode 100644
index 0000000..96eaec3
--- /dev/null
+++ b/stint/private/compiletime_helpers.nim
@@ -0,0 +1,9 @@
+import ./datatypes, ./uint_bitwise_ops
+
+func getByte*(x: SomeInteger, pos: int): byte {.compileTime.} =
+  type DT = type x
+  byte((x shr (pos * 8)) and 0xFF.DT)
+
+func getByte*(x: UintImpl | IntImpl, pos: int): byte {.compileTime.} =
+  type DT = type x.leastSignificantWord
+  byte((x shr (pos * 8)).leastSignificantWord and 0xFF.DT)
diff --git a/stint/private/endians2_priv.nim b/stint/private/endians2_priv.nim
index cf3a53e..812be23 100644
--- a/stint/private/endians2_priv.nim
+++ b/stint/private/endians2_priv.nim
@@ -1,5 +1,4 @@
-import ./bitops2_priv, ./datatypes, ./uint_bitwise_ops
-
+import ./bitops2_priv, ./datatypes, ./compiletime_helpers
 import stew/endians2
 export endians2
 
@@ -9,25 +8,21 @@ func swapBytes*(x: UintImpl): UintImpl {.inline.} =
 
   UintImpl(hi: hi, lo: lo)
 
-func copyMem(x: UintImpl): auto {.compileTime.} =
+func copyMem(x: UintImpl, ret: var openArray[byte]) {.compileTime.} =
   const size = bitsof(x) div 8
-  var ret: array[size, byte]
-
   type DT = type x.leastSignificantWord
   for i in 0 ..< size:
-    let pos = i * 8
-    ret[i] = byte((x shr pos).leastSignificantWord and 0xFF.DT)
-  ret
+    ret[i] = x.getByte(i)
 
 func toBytes*(x: UintImpl, endian: Endianness = system.cpuEndian): auto {.inline.} =
   # TODO can't use bitsof in return type (compiler bug?), hence return auto
   var ret: array[bitsof(x) div 8, byte]
   when nimvm:
     if endian == system.cpuEndian:
-      ret = copyMem(x)
+      copyMem(x, ret)
     else:
       let v = swapBytes(x)
-      ret = copyMem(v)
+      copyMem(v, ret)
   else:
     if endian == system.cpuEndian:
       copyMem(addr ret[0], unsafeAddr x, ret.len)